Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems.

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Structures in geological samples are often interpreted as fossilised life; however, such interpretations are equivocal, as abiotic processes can be invoked to explain their presence. Thus, additional lines of chemical evidence are invaluable in confirming or refuting such morphological evidence. Glass shards in tuff from the Ontong Java Plateau (OJP) contain microtubular structures that are in close proximity to functionalised nitrogen substituted aromatic compounds that may be indicative of the chemical remnants of biological activity. The organic composition of the OJP tuff containing microtubular alteration structures was compared with tuff without such features. In addition, organic matter associated with horizons with compacted remnants of woody material buried in the OJP tuff and overlying pelagic calcareous foraminifer sediment were also characterised, to ascertain the provenance of the organic matter found in the OJP tuff. As a further control, the organic material in submarine and terrestrial basalts from other locations were also characterised providing further evidence to support the view that the organic matter in the OJP tuff is authigenic. Carbon–nitrogen chemistry was detected across all OJP tuff samples irrespective of the presence or absence of microtubular features, but was not detected in either the wood material, the overlying pelagic sediments or in the basalts from other locations. The results indicate no direct link between the OJP nitrogenous organic compounds and the presence or absence of microtubular features.

Decontamination of geological samples by gas cluster ion beam etching or ultra violet/ozone.

Marine and terrestrial sediments stabilise organic carbon (OC) against microbial respiration, influencing the climate by slowing the release of CO2 into the atmosphere. Redox-active element-bearing minerals, such as the manganese oxide mineral birnessite (δMnO2) play an important role in OC stabilisation. However, the mechanism for birnessite-OC stabilisation is unclear, limiting further understanding of the role of birnessite in the carbon cycle. We hypothesise that bond formation is promoted on δMnO2 surfaces, ultimately producing a complex assembly of stabilised OC. We test our hypothesis by investigating δMnO2 samples spanning < 1 year to 2.5 billion years old, using X-ray photoelectron spectroscopy and thermogravimetric analysis to synergistically observe OC thermal decomposition. We propose that thermally stable OC is generated during δMnO2 reduction. We speculate that thermally stable OC is unsuitable for rapid microbial respiration and is therefore chronologically stable. We conclude that the OC stabilisation described here could be an important but hitherto unrecognised process that removes OC from the readily exchangeable OC pool, thereby helping to modulate the climate.

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&lt;p&gt;The procedures for detecting fossils on Mars can be derived from the methods that are already used in terrestrial paleobiology (Cady et al., 2003). Here fossils preserving regions are visually located, then inspected for morphological features that might imply fossilised biology (Cady and Noffke, 2009; Westall et al., 2015). Morphological evidence of microfossils on its own is not a completely reliable biosignature (Garc&amp;#237;a Ruiz et al., 2002).&amp;#160; However, evidence of biological activity may be implanted within the molecular and isotopic composition of organic compounds, which can serve as biosignatures (Summons et al., 2008). Thus, combining both morphological with organo-geochemical evidence could strengthen any argument that a given geological feature could be associated with biological activity. The results from the simultaneous morphological and geochemical analysis of geobiological structures on Earth could provide evidence that any comparable structures that may be observed on Mars, are potentially connected to biological activity, and therefore, may be suitable for collection for return to the Earth, for further analysis.&lt;/p&gt;&lt;p&gt;As a proof of concept, the distribution of the organic material that is associated with distinctive microtubules in the glassy volcaniclastic shards within tuff, that have been suggested to be putative ichnofossils (Banergee and Muehlenbachs, 2003), these were analysed by us using X-ray photoelectron spectroscopy, nanoSIMS and the Ionoptika J105 time of flight secondary ion mass spectrometer, with&amp;#160; an argon gas cluster ion beam. This indicated that nitrogenous organic material occurred in regions of the sample that were rich in microtubule textures and in the surrounding microfractures (Sano et al., 2016).&amp;#160;&lt;/p&gt;&lt;p&gt;These results demonstrated that the J105 ToF-SIMS combined with XPS and GC/MS analysis is able to match geomorphological features with their organic and inorganic composition at the &amp;#181;m scale, which may be a useful approach for the identification of fossilised life on Mars.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Banerjee et al., (2003).&amp;#160;Geochemistry, Geophysics, Geosystems,&amp;#160;4(4).&lt;/p&gt;&lt;p&gt;Cady et al., (2003). Astrobiology,&amp;#160;3(2), pp.351-368.&lt;/p&gt;&lt;p&gt;Cady et al., (2009).&amp;#160;GSA Today,&amp;#160;19(11).&lt;/p&gt;&lt;p&gt;Garc&amp;#237;a Ruiz et al., (2002).&amp;#160;Astrobiology,&amp;#160;2(3), pp.353-369.&lt;/p&gt;&lt;p&gt;Summons et al., (2008) Astrobiology, 90, 1151&amp;#8211;1154.&lt;/p&gt;&lt;p&gt;Westall, F., et al., (2015).&amp;#160;Astrobiology,&amp;#160;15(11), pp.998-1029.&lt;/p&gt;&lt;p&gt;Sano, N et al., (2016).&amp;#160;J. of Vac Sci &amp; Tech A: 34(4), p.041405&lt;/p&gt;